\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}
	C <box>dV<sub>out</sub><over>dt</box> = I<sub>b</sub>
	&tanh;(<box>κ(V<sub>in</sub>-V<sub>out</sub>)<over>2</box>)
\end{equation*}
\end{document}
